DFSO is a mode to improve fuel economy and reduce brake wear in a motor vehicles. In this approach, fuel injection to one or more cylinders is shut off during selected operating conditions. Such conditions include a state in which the driver's intention to decelerate is detected. Besides intention to decelerate, other factors may determine whether or not DFSO is enabled. In some motor-vehicle configurations, DFSO is enabled only at the highest gears of the transmission—e.g., fifth and sixth gear of a six-speed transmission. DFSO may be disabled at lower gears and lower vehicle speeds to avoid excessive deceleration due to increased drive-line torque in the lower gears. In some cases, DFSO initiated in a lower gear or persisting across a coasting downshift may cause non-intuitive deceleration relative to vehicle speed or an excessive increase in the deceleration rate across a downshift, which is undesirable during most driving conditions.
The inventors herein have observed, however, that appropriate conditions for DFSO depend on other motor-vehicle parameters besides driver intention, vehicle speed and transmission gear. Such parameters include driven mass, driven wheel size, and road load, as examples. Because the driver interacts with the vehicle vis-à-vis the deceleration rate when coasting or braking, the impact of DFSO on vehicle deceleration will be affected by these other parameters. Depending on the values of the parameters, it may be desirable to enable DFSO at lower gears and through additional coasting downshifts, to extend the fuel-economy and brake-wear benefits of DFSO to a wider range of operating conditions, while providing desirable vehicle deceleration for the driver. Moreover, as driven mass, wheel diameter, and road load may vary for the same motor vehicle in different usage scenarios—e.g., towing/not towing, large payload and passenger load or unloaded, on- and off-roading—it may be desirable to provide automatic adjustment of DFSO as operating conditions change.
Accordingly, one embodiment of this disclosure provides a method for enacting DFSO in a motor vehicle having an engine and a transmission. The method includes, during a condition of normal engine-braking efficiency, disabling the DFSO below a higher gear of the transmission. During a condition of reduced engine-braking efficiency the DFSO is disabled below a lower gear of the transmission. In this manner, the fuel-economy and brake-wear benefits of DFSO are extended to a wider range of operating conditions.
The summary above is provided to introduce a selected part of this disclosure in simplified form, not to identify key or essential features. The claimed subject matter, defined by the claims, is limited neither to the content of this summary nor to implementations that address the problems or disadvantages noted herein.